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"Learn from me, if not by my precepts, at least by my example, how dangerous is the acquirement of knowledge, and how much happier that man is who believes his native town to be the world, than he who aspires to become greater than his nature will allow."

In Fullmetal Alchemist, performing a forbidden human transmutation will take you to the Gate, where, along with being maimed in some way, you get to look inside and see 'Truth', which, as Izumi stated, looked like hell to her.

Almost all alchemists die doing so. It is implied by Izumi that just surviving it is a very serious feat. Alphonse would have died if his brother had not brought him back. By the end of the story it is revealed that Father was unable to find enough living alchemists who have survived that as required for his Evil Plan to work.

Also, learning that the Philosopher's Stone is created by sacrificing mass numbers of human lives has driven many who have sought its power insane. In the 2003 anime version, Scar's brother was one of the people thusly afflicted.

Zeref of Fairy Tail is the living proof of what happens when you delve too deeply into taboo magic. He wanted desperately to bring his younger brother Natsu Back from the Dead, and in the process not only studied various forbidden magics, but also created several magical theories most sane mages would never touch. The price? He was cursed to kill anybody he could ever care about or even being in the same general area as him, with immortality to boot as well as live long enough to see many of his works be misused. However, this immortality also bought him time to succeed in his original goal of bringing his brother back, and he didn't become evil until much later. After that, his continued studies into the taboo were to find a way to kill himselfwhich he eventually figured out.

Comic Books

When Doctor Strange meets the Living Tribunal (the most powerful being in the Marvel Universe who isn't God), he shows Strange how the Universe was created. Strange quickly averts his eyes, paraphrasing this trope.

When Spider-Man helped Doctor Strange fight off an attempt by Doctor Doom and Dormammu to bring about an event called the Bend Sinister, Spider-Man asked Strange what a Bend Sinister was, only for Strange to say, "There are things that man was not meant to know." Spider-Man didn't take it too well.

John Byrne's "Trial of Galactus" arc in Fantastic Four ended this way when Byrne wrote himself into the final issue. The Watcher snatched him from his home and brought him to the cosmic tribunal, stating that he was the "chronicler" of the Fantastic Four's adventures and thus needed to be there to witness as Reed Richards was brought to trial for the destruction of the Skrull throneworld; he was accused of genocide because he saved the life of Galactus some time before. Various cosmic beings, including Galactus himself and Odin, arrived to testify on Reed's behalf. In the end, Eternity showed everyone assembled the True Purpose of Galactus. The last page had the Watcher warning Byrne that as he wrote this story, many of the details would escape his memory, as the human mind wasn't meant to hold such knowledge.

In The DCU, the Anti-Life Equation is a mathematical proof that life, hope and freedom are all pointless. Any sentient being who's forced to comprehend the Equation instantly becomes a mindless drone. Darkseid's ultimate goal is to rule the Omniverse with this.

In Ultimate Spider-Man, Spidey has something of an existential crisis after a brief brush with the supernatural, saying later that he's "Seeing things he shouldn't." The inciting incident was actually a relatively tame (by reader standards) vampire story, but his seemingly outsize reaction reminds us of how mentally devastating commonplace fictional tropes would be if ever actually encountered.

In War World, Superman once had to catch Supergirl, who at the end of the previous adventure had been hurtling unconscious through the dimensions. The Spectre tried to stop him from pursuing; naturally he fights back; and naturally he can't even budge the Spectre physically or otherwise. Eventually the Spectre convinces Superman that following Supergirl would lead him into realms that no mortal should witness (implied to be Heaven. Supergirl was unconscious, so it wasn't a problem for her.) When Superman asks for the Spectre's help, he responds "Of course; you only had to ask," and simply teleports Supergirl to them.

In The Vow, the destructive potential of fireworks that Lord Shen starts researching obsessively is regarded as this by his parents and the Soothsayer. It is for that reason Shen's parents haven't researched fireworks further as they are dangerous already when used to entertain people.

Referenced in a fanfic called "Remus Lupin, P.I.". Someone's death is put down to "Meddling with that which wizards were not meant to know." It's noted as being the third-most-common cause of accidental death in the wizarding community.

The Sanctuary Telepath: the "how it could have been" projection and the time machine.

Janine: I saw the apocalypse and I felt like it was worth it because we were together. This is not right. Humanity was never supposed to have this kind of power.

She also considers the original experiment to fall in this category.

Janine: We messed with nature and we thought we could get away with it. We payed the price.

The true nature of the Shadows Who Watch, Make, and Rule, beings beyond even the Elders, is this, as Celestia refuses to divulge what they are because it'd likely drive a normal pony insane. Nyarlathotrot and his twin Fillimon are the Anthropomorphic Personification of their dark side and light side respectively. They're the Readers, Writers, and Hasbro. It's implied Celestia, Luna, Discord, and the other gods are all aware of a lot of these, being deities who helped make the universe.

The Outer Concepts literally are this. Their entire purpose for existing is to give mortals a healthy fear of the unknown so they don't accidentally tamper beyond their death for the good of themselves and existence.

Film — Live-Action

In the movie π, the protagonist Max is on the verge of unlocking the pattern of the universe using a 216-digit number. A group of Orthodox Jews believes that the number is the true name of God, while a stock broker wants it to predict the stock market. However, the number overwhelms anyone or anything that tries to compute it. Max, who already stared too long at the sun and did permanent damage to his brain, begins to completely break down as he studies the number. His computer breaks down and starts creating organic goo. Ultimately Max abandons his quest and chooses to simply live life in ignorance, possibly drilling out his mathematical genius to escape the number's curse.

After seeing the title creature in The Abominable Snowman, the native guide exclaims that he has seen "what man was not meant to see!" and flees back to his village. This is ultimately subverted, as the yeti are actually peaceful beings who just scare people off to protect themselves.

In Batman v Superman: Dawn of Justice, when Lex Luthor begins to use the crashed Kryptonian ship to create a "Kryptonian Deformity" out of Zod's corpse and his own blood, the ship's A.I. is quick to warn him that such an act was considered this on Krypton. Luthor being Luthor, he goes ahead with it anyway.

Captain America: The First Avenger: The religious order hide the Tesseract because they feel it's "not for the eyes of ordinary men". Unfortunately for everyone else, the Red Skull doesn't apply as "ordinary".

In Interstellar, this phrase is said almost verbatim by one of the astronauts, when talking about the interior of a black hole's event horizon, but to all appearances he's just being over-dramatic about astrophysics. He's wrong, but not for the obvious reasons: there is something in there, and man was meant to know...

Optimus Prime: There are mysteries to the universe we were never meant to solve, but who we are and why we are here are not among them. Those answers we carry inside. I am Optimus Prime, and this message is to my Creators. Leave planet Earth alone. 'Cause I'm coming...for you.

Literature

There's a story by Isaac Asimov where a man with access to a super computer that can tell you anything if you know how to ask tries to discover the source of humor. He tries because he himself is a wonderful, though nonprofessional, comedian. Eventually it turns out the sense of humor was an alien experiment that would be halted as soon as anyone figured out that it was so, meaning he destroyed everyone's sense of humor. Plus, the aliens will now replace humor with something else. Who knows what?

The protagonist of the Boojumverse story "The Wreck of the Charles Dexter Ward" had previously dabbled in so-called forbidden science, unafraid of the consequences. After what she witnesses aboard the Charles Dexter Ward, however, she decides that there are indeed certain areas of knowledge that man was never meant to meddle in.

In A Brother's Price, the fact that male babies are often stillborn is somewhat treated like this, with women saying "Not in front of the menfolk" when someone tries to discuss it with men nearby. While it doesn't drive anyone crazy to know about it, hearing a woman talk about how her stillborn son was perfect right down to his beautiful little blue toes, just, you know, dead is quite creepy.

In the Robert A. Heinlein short story By His Bootstraps, Bob Wilson sees one of the High Ones through a time viewer and almost loses his mind. It was the emotions the High One was feeling that caused his discomfort - an overwhelming mixture of sadness, tragedy, grief and weariness.

"He drove me from him at last, saying that I was but a common witch in spite of his teachings, and not fit to command the mighty sorcery he would have taught me. He would have made me queen of the world and ruled the nations through me, he said, but I was only a harlot of darkness. But what of it? I could never endure to seclude myself in a golden tower, and spend the long hours staring into a crystal globe, mumbling over incantations written on serpent's skin in the blood of virgins, poring over musty volumes in forgotten languages. "He said I was but an earthly sprite, knowing naught of the deeper gulfs of cosmic sorcery. Well, this world contains all I desire—power, and pomp, and glittering pageantry, handsome men and soft women for my paramours and my slaves."

The Igors of Discworld's Thief of Time, strictly speaking don't believe that there are TMWNMTK, but even they find some obvious stuff that they'd rather not know, such as how it feels to have every single particle of your body sucked through a small hole.

In Turn Coat, Harry uses his Wizard's Sightnote A special ability that lets a wizard see things as they are, for the low, low cost of never being able to forget it to figure out what exactly is following him. He glimpses the Skinwalker...and comes back to himself about three minutes later, having almost crashed his car, gibbering uncontrollably. He gets himself under control, tries to remember what he saw...and comes back to himself five minutes later, incoherent and barely in control of himself. He realizes that driving is a bad idea, gets out of his car and starts walking to get help when his thoughts just barely brush against the idea of what he saw... and he comes back to himself, curled into a fetal position on the sidewalk, crying and in physical pain.

In a more traditional example, the Seven Laws of Magic define the types of addictive Black Magic that can corrupt a spellcaster into a downward cycle of psychosis. There's one against killing people with magic, one against raising the dead, and one against Mind Control, for example. The Seventh Law puts even trying to learn about Outsiders on par with all of the above.

A young Harry once interacted with an Outsider for all of fifteen minutes. His description of encountering it normally is nearly as bad as his description of the skinwalker through the Sightnote Both can be found on the Quotes.Eldritch Abomination page, if you're up for some Nightmare Fuel, and it left a psychic scar that's still visible years later.

Harry Potter: "There is a room in the Department of Mysteries that is kept locked at all times. It contains a force that is at once more wonderful and more terrible than death, than human intelligence, than the forces of nature. It is also, perhaps, the most mysterious of the many subjects for study that reside there. It is the power held within that room that you possess in such quantities and which Voldemort has not at all."

According to The Guide, there's a theory that if any one person ends up knowing both the Ultimate Answer and the Ultimate Question, the universe will end and be replaced by something even more bizarre and incomprehensible. There are other theories that state that this has already happened several times.

The Restaurant at the End of the Universe: The most horrible torture device in the normal universe is the Infinite Perspective Vortex, which works by showing you the whole universe, and how insignificant you are. And it's powered by a fairy cake. It IS possible to survive the Infinite Perspective Vortex by being the most important person in the (current) universe, but you'll walk away an even bigger Jerk Ass after being told by a machine that the universe revolves around you.

Give a witness too much truth serum, in a court, and he'll tell "the whole truth". ALL of it. Oddly enough, the guy who comes to know all the truth doesn't seem to become mad (mostly) - those who hear from him, though, do. This may be because he knows all the truth, whereas the listeners only know the part they hear. Oddly enough again, most of the good bits are about frogs.

E. Nesbit's short story Hurst of Hurstcote uses the trope name almost verbatim. Two characters are discussing a sort of mesmerism, and ponder the difference between "things man was not meant to know" and "things man was meant not to know".

In the Stephen King short story "The Jaunt", teleportation is possible... but you'd better be unconscious when you do it. Anyone who goes through the process awake is driven completely insane and often dies. The man they tested it on managed to croak out "it's eternity in there" before dying. The story follows a family who is about to Jaunt to Mars. Their father tells them the history of the Jaunt process to kill the time before it is their turn, and when they go through, the young son holds his breath when the knockout gas is administered. A split second later, on the other side, his hair has gone completely white and the boy is quite mad, cackling that the Jaunt was much longer than anyone thinks before he rips his own eyes out.

Similarly, in The Langoliers, anyone who passes through the time rip while awake ends up being disintegrated.

The magic of Naming in The Kingkiller Chronicle requires the Namer to gain an intuitive understanding of the target, grasping everything in its history that shaped it into what it is. This is explicitly impossible for the conscious mind to handle. Namers slip into a passive state of Hyper Awareness to manage it, but the powerful ones tend to live a bit at odds with what most people consider real, and the University has a sizable asylum for the people who get too close to the subject material.

A book by Mike Kurland explains the protagonist's attitude: "He had long ago decided that there were no Things Man Was Not Meant To Know. He was quite willing to concede, however, that there were Things Man Was Too Dumb To Figure Out."

H.P. Lovecraft's work tends to be full of things that should not be named or known to man. Some variant of the line "there are things in the world man was never meant to know" is frequently said near the end of his stories, just as the protagonist has some (literally) mind-blowing revelation about the nature of the universe and our place in it, or at the beginning when he starts to recount his story that ends like that.

Ironically, while the "forbidden" knowledge in Lovecraft's tales is often at least disturbing and at times outright dangerous (especially when there are forces at work that actively go out of their way to eliminate people who might know too much), upon closer reading ignorance affords his characters no protection either — quite a few come to bad ends precisely because they don't know enough about what they're dealing with. Damned if you do...

In "Macroscope" by Piers Anthony, use of the title machine accesses a mathematical sequence which is shown to whomever uses the device. It destroys the intelligence of anyone above a certain IQ who hasn't evolved beyond violent tendencies.

In Algernon Blackwood's "The Man Who Found Out", an explorer discovers the long-lost Tablets of the Gods, reputed to explain the true purpose of human existence. Reading their translation causes him to lose the will to live, and the friend who inherits the Tablets destroys the text and has his own memory of reading it erased via hypnosis.

"The Subject Is Closed", a Larry Niven short story set in The Draco Tavern, involves a priest asking one of the ubiquitous Chirpsithtra (who seem to know everything about anything) about the existence of God. The Chirp responds with a story of a race of beings who set about to prove the non/existence of an afterlife. The Chirps lost contact with them and the next time a trade ship visited, they found the entire race had calmly and orderly committed suicide. Whatever they had discovered, it was something that had convinced the entire race they were better off dead, and something the Chirps were not particularly interested in knowing. Rick later explained relating this particular story was the Chirp's way of politely saying "none of your business."

Paradise Lost: The angel Raphael answers all of Adam's questions about the War in Heaven, the creation of the world, and the laws of the cosmos (although he doesn't find knowledge of the latter at all practical or useful for humans), but when Adam asks him if angels express love, like humans, Raphael blushes "celestial rosie red" and quickly explains that yes, angels "love," too. How? Whoah, look at the sun, time to go! Live long and prosper!

Played with in the ST:TNG novel Metamorphosis. Watching Geordi's frustration at being unable to determine how an alien artifact works, Data suggests that they were not meant to know. After Geordi both rejects the idea and expresses disgust at Data of all people proposing a mystical explanation for something, Data explains that he means the artifact's creators may have designed it so that its inner workings could not be analyzed.

The second of Henry Spencer's "Ten Commandments for C Programmers" is, "Thou shalt not follow the NULL pointer, for chaos and madness await thee at the end." (Reading data from a null pointer is a very common programming error in C, and was particularly notorious at the time because it had predictable and harmless results on certain platforms but caused others to immediately crash.)

20,000 Leagues Under the Sea: For the man of the 19th century, reaching the South Pole would be something man was not meant to achieve. In this novel, is lampshaded by Ned Land's opinion about the beauty of the South Pole’s icebergs (and those words are said just before the Nautilus is trapped by them and the crew is soon Almost Out of Oxygen).

"it's a wonderful sight! Isn't it, Ned?" "Oh damnation, yes!" Ned Land shot back. "It's superb! I'm furious that I have to admit it. Nobody has ever seen the like. But this sight could cost us dearly. And in all honesty, I think we're looking at things God never intended for human eyes."

In Warrior Cats, the existence of SkyClan, an exiled fifth Clan, is kept secret from all cats ( Well, at least until the sixth story arc.) until they die and join StarClan, since StarClan feels too guilty about how SkyCLan was driven out. Upon learning of SkyClan, Firestar is so shocked he nearly loses faith in StarClan altogether,

Live-Action TV

On Babylon 5, a Dilgar war criminal buys her way out of prosecution by offering the formula for an immortality serum. The catch is that the formula's ingredients must be fatally extracted from sentient beings, making it a surefire trigger for mass murder and a thing Sentient Beings Were Not Meant To Know. The Vorlons, fortunately, agreed.

Also on B5, apparently nearly every sentient race has developed a dish almost identical to Swedish meatballs, when G'Kar comments on this, his response is.

"It is one of the great mysteries of the universe, that we will either never know the answer to, or which would drive you quite mad if you did."

Another one from G'Kar: "There are things in the universe billions of years older than either of our races. They're vast, timeless, and if they're aware of us at all, it is as little more than ants, and we have as much chance of communicating with them as an ant has with us. We know, we've tried, and we've learned that we can either stay out from underfoot or be stepped on. [...] they are a mystery. And I am both terrified and reassured to know that there are still wonders in the universe, that we have not yet explained everything."

In Battlestar Galactica, the Final Five are treated like things Cylons are not meant to know. D'Anna Biers grows an obsession with them, repeatedly committing suicide to glimpse into the place between life and death in a quest to find out about them. When she finally does get a glimpse, it results with her suffering from Psychic Nosebleed, followed by death.

Possibly subverted though. The Final Five were rendered things-Cylons-are-not-meant-to-know because Model One/Cavil made them so. Their origins are far more mundane than the Cylons think.

In Being Human, there is a secret only the dead know. When Annie tells this secret to Owen, her murderer, it torments him, driving him to confess his crimes.

Beyond: Arthur believes journeying into the Realm (in the belief it's the afterlife, which living people can visit) is a very bad idea. He appears to be right, as it's not only unclear if the Realm really is the afterlife, but there are dangerous things there which do not want people of our world visiting.

"Journey's End": Donna gets caught in the Meta-Crisis which creates a second Doctor, who as a result becomes part-Human, while she gained a Time Lord mind. Unfortunately, it's a Brown Note, as over 900 years of Time Lord knowledge and experience shoved into her human brain almost kills her. To save her life, the Doctor has to permanently lock away all memory of him from her conscious mind.

The Silence are a religious order, who believe that if the Doctor's true name is ever spoken, it will lead to the end of the universe. Knowing that he will be asked "The Question" on the Fields of Trenzalore, where he must answer truthfully, they plan to kill him before he ever ends up there.

"Extremis": The Vatican has in its possession a Tome of Eldritch Lore called The Veritas, Latin for "truth". The truth revealed in the book is so horrible everyone who reads it is Driven to Suicide. What is that truth? The world is a computer simulation created by hostile aliens in preparation for their invasion of Earth.

In Stargate SG-1 the Ancients' Repository of Knowledge devices (Jack referred to them as Ancient head suckers because of the way they latch onto the user's head) can download the entire knowledge bank of the Ancients into the mind of the user, however said information is too vast for the human mind to comprehend at our current evolutionary level. Therefore anyone exposed to the knowledge bank will have their minds completely taken over by it causing them to degrade and eventually shut down (die). Jack had his head sucked twice, and while he was able to build many advanced technologies, he was eventually unable to speak or comprehend anything other than the Ancient language and he nearly died from the strain on his brain- the second time he had to go into stasis to escape death.

The Twilight Zone (1985) episode "Need to Know" concerns a phrase which passes from person to person like a disease, explains the meaning of existence and drives a small town mad.

The Illuminati New World Order card game has a card called "Secrets Man Was Not Meant to Know". There was a gag card appropriately titled "Secrets Man Was Not Meant to Know In the Biblical Sense".

GURPS IOU (Illuminati University) had a class in the Thaumaturgy department called "Things Men Were Not Meant to Know". There's also a class in "Men Things Were Not Meant to Know". Also, what the O in IOU stands for is a closely-guarded secret.

Appropriately, Munchkin Cthulhu has a card called "Learn Things Man Was Not Meant to Know: Go Up a Level."

The Truth, upon which the World of Progress in SLA Industries is precariously balanced, can be used to grant incredible power to anyone who knows it and understands how to manipulate it. Most people — upon discovering it — are driven infinitely insane and/or die horribly. It's been stated that if enough people discovered The Truth, the entire universe would disappear in a puff of logic and cease to exist...

Mage: The Awakening's Guardians of the Veil justify many of their actions with the idea that there are plenty of things that man was not meant to know (and not quite as many things which even mages shouldn't). They are often at odds with the Mysterium, who believe man is supposed to know everything, and both orders are at odds with the Free Council, who believe man should know everything right now.

There's a Legacy, the Logophages, devoted entirely to this idea — it's their job to not only track down the things man must not know, but to make sure they remain unknown, even to themselves. Needless to say, they're masters of memory alteration and occasionally give their own brain a good scrubbing just in case.

As for specific things not to know, well... there's the Nemesis Continuum, a set of Abyssal mathematical proofs. Once you grasp one, it's easier to know the others, and as you learn them, the physical laws they represent begin to overwrite the real world. By the time you realize that the color green has become searing-hot or that gravity now functions the way Aristotle described it as opposed to the way it's supposed to, it may be too late to correct that...

The most active greater Abyssal power, the Prince of Ten Thousand Leaves, is a self-aware Alternate History that inserts snippets of itself into texts and becomes more real where those texts are brought together. A cult in Massachusetts has made a collection into a Tome of Eldritch Lore, which has started to warp their town into an Eldritch Location and mutate the townsfolk who memorize too much. If the entire Prince is assembled, it Cosmic Retcons itself into having always been real.

Call of Cthulhu. Everything in the game is full of things man (and woman) was not meant to know, and so you are eventually either incredibly ignorant or incredibly insane. Maybe both simultaneously.

Maybe the most common CoC joke is just the single sentence "I read the book".

In Exalted a demon exists called Orabilis; his title is The End of All Wisdom. He builds libraries, and it is his will that demons and men read in them and grow wise...but not too wise. Sometimes people take two and two, though, and learn a thing mean only for the Yozis; at that point, he's free to pursue you out of Hell, drag you back, and cast you into the sky where you spend a thousand years as a dying star. Deconstructed, in that the Things Man Was Not Meant to Know were pretty arbitrarily decided by the Abusive Precursors, and they're actually scared of their secrets getting out. They're only Not Meant To Know because the Yozis Don't Want You To Know Them.

The Works by Phil Foglio features Agatha Heterodyne reading a book titled "Things Man Was Not Meant To Know"... and looking less than impressed, since she is a woman.

Cthulhu 500, a racing car cardgame, has this in spades. (It is Cthulhu, after all.) You can drive The Car Man Was Not Meant To Drive, equipped with The Wheels Man Was Not Meant To Mount and The Mudflaps Man Was Not Meant To Ogle, all paid for by The Sponsor That Must Not Be Named.

A lot about the world in KULT. OTOH, you have to learn this if you want to break free from it.

In the World Of Warcraft tabletop RPG, the ability to speak and write in the demonic language will slowly eat away at the sanity of mortals who dare to learn it. Characters who possess this forbidden knowledge must make a saving throw every year, with each failure resulting in the permanent loss of a wisdom point. Meaning that unless you have consistently good rolls your character will eventually go insane and die.

In the Rifts Atlantis Sourcebook, there is a permanently open Rift in the pyramid at the Azlum the Asylum, which leads to a dimension of pure light. No one knows what is on the other side, anyone who looks directly into the Rift goes insane (hence the Asylum), changes Character Alignment, and gains Psychic Powers.

Toys

Happens to Lariska when Tren KromMind Rapes her in BIONICLE, as his search for information in her mind also causes her to get glimpses into his mind. A similar experience happened to Makuta Mutran thousands of years prior when Teridax sent him to find Tren Krom to gain vital information for his plan to usurp Mata Nui. He succeeded...but didn't come out quite the same.

Video Games

Diablo II plays this one straight when Marius witnesses Diablo's transformation. He even says it "was not meant for mortal eyes."

Eternal Darkness: Sanity's Requiem plays on this trope with one of the characters going insane (well he wasn't really but he sure sounded like it) after seeing "beyond the veil".

Oh...oh gibbering insanity wrought in flesh as though an artist sculpted it! Created from nothing by their mistress Xel'lotath, a canvas as grotesque as any!! Their bodies made no sense - no heads, no organs - an empty husk devoid of the trappings of nature... But it walked...it sang...it shrieked!!! A mockery of reason, both natural and mental!! A blasphemy from beyond the Veil!! The veil has opened!! And we should not see beyond!! We...we weren't meant to...never...ever...meant to!! Oh, give us the blessing of ignorance, the happiness of oblivion... Innocence can only be tainted, never returned!

In La-Mulana, the Skimpy Swimsuit—and a nice screen-sized shot of Lemeza wearing it—is your final reward for beating Hell Temple. Duracuets warns you on multiple occasions that the reward was not meant to be seen and that you may regret obtaining it.

Rayman 3: Hoodlum Havoc features a weaponized thing Man (or rather, a cute little fairy-like species) was not meant to know. There is a secret so horrible that it corrupts anyone who hears it. A single member of the species somehow learned it, and he captures others and whispers it to them, then lets them whisper it to others, like an intellectual Zombie Apocalypse. It'd be horrific if the entire game weren't Played for Laughs.

Elizabeth/Theo: "There are things your kind is better off not knowing." So I've been taught, which means... I mustn't... But using THAT for cooking...

Also invoked by Mitsuru when asked about the punishment for Mr. Ekoda. She simply states, "There are things in life you are better off not knowing" with a completely straight face.

The Bureau's interrogation and torturing techniques in Escape Velocity: Nova are alluded to but never explained. All that other characters will say of them is that they are "sickening" and too horrible to describe. In one plot line, the player is captured and suffers it first-hand: The game dialogue will only tell you that what you experienced is too awful to remember, and that for the rest of your life whenever you even attempt to recall what you have been through, you will lapse into incoherent, terrified screaming.

Call of Cthulhu: Dark Corners of the Earth has the main character, a private detective, progressively learn more and more of these until he discovers he has been time-switched by the Great Race of Yith (a la A Resection of Time) which contributes to his suicide.

There exists... something... in Star Control II that causes horrible death to anyone who learns about it. Maybe. This happened to the Androsynth, and to one scientist in your landing party, who read their science notes leading up to the event (except you don't lose a crew member). It is repeatedly stated by those in the know that ignorance is the best defense against this thing, as it cannot affect anyone who doesn't know about it. A race of Eldritch Abomination aliens - the "fingers" of something else's "hand" - mysteriously appeared nearby around the same time. But they don't like it if you ask too much about what happened.

The eponymous Elder Scrolls themselves are this, combined with being Tomes of Prophecy and Fate. Referred to as "Fragments of Creation," the scrolls are of unknown origin and number which simultaneously record past, present, and future events irrefutably; what did happen, what could have happened, what might yet happen. Even the falsehoods in them are true. (Especially the falsehoods, as is pointed out several times in the series.) To the untrained eye, the scrolls will yield an odd chart that looks like it has constellations on it with odd glyphs printed over or under it. A knowledgeable reader will be able to interpret the scrolls to a degree, but incompletely, and will be irrevocably struck blind. A well-trained reader, such as a member of the Cult of the Ancestor Moth, will glean much more from the scroll and will even recover their eyesight... for a finite number of times before their sight is permanently lost. In all of these cases, reading the scrolls tends to lead to madness for the user. Even those who merely study the scrolls, never actually using or even handling them, are driven to complete madness with alarming regularity.

The Daedric Prince Hermaeus Mora has this trope within his sphere. Appropriately, he is also the only Daedric Prince to actually take the form of an Eldritch Abomination, being an endless mass of tentacles and eyes. If there exists some bit of information in all of existence which he does not know, he will mercilessly acquire it by whatever means necessary. One in-game book describes a mage who tried to explore the realms of Oblivion. When he entered Hermaeus Mora's realm of Apocrypha, an endless library, he became enamored with the knowledge and never left. His voice still whispers to the writer, each time more and more alien. Further, according to Mora himself, he is/arose from knowledge that cannot exist (detritus concepts ejected from reality), rendering him not only the keeper of things man was not meant to know, but also making him something man cannot know.

The Hist are a race of ancient, sentient, and possibly Omniscient trees native to the Black Marsh where they are worshiped by the Argonians. They are said to possess "unfathomable" knowledge from the Dawn Era, the earliest days of creation before linear time existed as a concept.

Sotha Sil: "The Tools of Kagrenac in your possession? I think not. Were you to have them, I would fear for your life. They are not tools for mortals, Fyr, as you well know."

Oblivion: "I have seen the Gates of Oblivion, beyond which no waking eye may see."

Skyrim goes in depth about how the Dwemer used to build giant magical computers powered by Elder Scrolls and starlight. They catalogued what they could interpret from the Elder Scrolls into cube-shaped storage devices and simply touching one of those devices can drive a person to insanity. The Dwemer themselves, in the series backstory, attempted to use this information to Ascended to a Higher Plane of Existence. Whatever happened, success or failure, caused their entire race to disappear from the face of Nirn in an instant.

"There are things I need of you. Things you may not understand, and may not wish to do, but please, do not make the same mistakes I did [...] Human nature sealed my downfall. My name is Philip. If we are lucky, then by the time you receive this, I will be dead. If fate frowns, we all perish"

In The Reconstruction, Falitza allegedly destroyed her mind by "peering into the unknown". Subverted, though — it's Obfuscating Insanity. She was so sick of being "little miss perfect" that she staged the whole thing to get thrown into Sanctifel.

In Dark Souls, the final part of Big Hat Logan's storyline if you rescue him and learn all of his sorceries has him going insane while trying to decipher and duplicate the spells of Seath the Scaleless, the dragon progenitor of sorcery.

Dark Souls II has the Darklurker, an enigmatic being which possesses power over various elements and resides in the deepest reaches of an Eldritch Location only accessible through a portal. Its flavour text outright states that some things would better be left unilluminated.

Bloodborne: This is a gameplay mechanic. Instead of Humanity, your character gains Insight on the way Otherworldly beings see Yarnham. By observing them with your insight, new enemies appear and old enemies gain advanced attacks, in addition to all the tentacled monsters that lounge in the background. It's... disturbing. Especially the constant wailing of a lost baby in the night... knowing now that you have to kill it before it achieves its true form. Ew.

In Mass Effect 3, the Leviathan DLC has the Leviathan admonish Shepard for not turning back when they warned them, managing to uncover the location they've spent over a billion years trying to hide, but even worse, having the sheer audacity to decide to venture into the depths of an ocean on an alien world, simply to confront them face-to-face!

Leviathan: You have come too far!

Played hilariously in the second Professor Layton game. One of the failed tea recipes leads to a startled Luke informing us that there is smoke rising from the cup, to which Layton responds, 'This is clearly a tea that should not have been.'

Fallen London has a particularly horrific variation in the "Seeking the Name" quest. Rather than the knowledge itself harming you, it's the process of seeking it, trying to find it, getting to the next scrap in a gigantic, endless trail of misery that destroys you and everything you have. The various things you have to do in order to advance will have you destroying your moral and social standing, your sanity, your body, your soul, among others, in possibly the most epic example of Press X to Die in videogames.

The Correspondence is this to a T. Not only is one glyph from it described as "punctuation. Protection. A legal token. An illegal weapon. A punchline. It's an odd language." But once your character has learned enough of it the glyph's will occasionally force themselves to the front of your characters mind and make them contemplate what they mean in full. Think that doesn't sound so bad? Several of the glyph's will spontaneously set the area around them (read: you) on fire. These are some of the tamer ones.

It gets better. The Correspondence's nasty effects are caused by writing them improperly, IE bad grammar. When used correctly it is a reality warping LANGUAGE. This is because it is the language of the Judgements, AKA the stars. They decide what is and what is not in their domains. In the Neath there is no Judgement keeping things normal. Which is why so manycrazythings exist down there, why so many people are crazy and why death is on extended leave.

Zig-zagged in Sunless Sea. The Name is still a foolish, haunted journey to the center of madness. The Name is still something humanity was never intended to know. However, this is a different Name than the above, and your ex-Dawn-Machine navigator knows what this particular Name is really good for - if you bring it to one of the very few not-totally-evil gods in the universe, they will reward you with Exaltation. The key here is that it's treated as a glorious journey undertaken for its own sake, even though the player must willingly and literally abandon everything that makes them human.

In Thaumcraft (a magic-themed Game Mod for Minecraft), certain research is classified as "forbidden knowledge", some knowledge being more forbidden than other knowledge. Researching this knowledge will give you "Warp", which sticks to you for the rest of the game. (And considering what game it's a mod for, that could be a while.) Having warp gives you effects of varying severity depending on how much you have, ranging from harmless paranoia-inducing messages ("Something is following you...") to being hunted by Eldritch Abominations.

Darkest Dungeon: Aside from the horrible bioengineered Eldritch Abominations that threaten the town in ways that defy creation, you end up discovering THE TRUTH: humanity was created by a cosmic horror known as the Heart of Darkness, possibly as an incubation regulator, or possibly by accident, and it nests in the hollow core of Earth so that their millions of children may one day be born by blowing up the planet. Half your party dies to kill ONE of them. ONE. A SINGLE BABY Heart of Darkness was enough to fuel, command, and control EVERYTHING wrong with your estate. The sheer horror of this truth drives the player character to suicide.

Halfway through Phantom Dust, the protagonist and the leaders of a group called the Visions learn that all of humanity that remains on Earth are nothing more than memory constructs created by the final human being before dying. Though the Protagonist, who was based on said human's best friend, had much more detail put into his creation, the others were rushed constructs who shatter and cease to exist upon witnessing the memory realizing their lives were essentially that of illusions.

The Nasuverse has the Mystic Eyes of Death Perception, a special ability which allows people to "see" death, in the form of lines across everything that can be cut through in order to instantly kill or break apart the object. However, not only is the human mind not meant to comprehend actually seeing the concept of death, the fact that the lines are literally everywhere constantly reminds the user of the fragility of everything that exists. The comprehension is enough that Shiki Ryougi, who was already borderline psychopathic before she got the eyes, immediately tried clawing out her eyes when she realized just what her eyes were seeing. Meanwhile, Shiki Tohno doesn't freak out nearly as badly initially, but continual use throughout the story degrades his health and strains his brain as his eyes get more powerful and start showing him the death of things he shouldn't normally be able to comprehend (like buildings and concepts).

A more mundane example in We Happy Few with the Very Bad Thing that the people of Wellington Wells did to defeat their German occupiers. Whatever it was, the moral guilt from enacting it drove the citizens so mad that they began taking Joy to forget. By the time the game starts, the entire town is out of their minds on Joy, and even the Wellies who have been taking it their whole lives will become Downers if they learn what the Very Bad Thing was.

Web Comics

The Spark in Girl Genius is pretty much made of this trope, a pool of knowledge about how the universe works on a fundamental level that, if the user is extremely educated and highly trained, only drives them temporarily insane and breaks reality. For users that aren't absurdly broadly educated, killing yourself and leveling the surrounding area like a small tactical nuke is considered the best outcome you can hope for. The Spark being fairly common has had an interesting effect on the landscape and politics of Europe.

Carson von Mekkhan: In my experience, a strong Heterodyne will take about two hours to truly warp the laws of nature.

ThisNodwick strip had entirely too much fun with this, as quoted above. The Thing Man Was Not Meant To Know was discovered by She Who Must Be Obeyed and taken back to The Lands That Know No Name! ("Let me know if we stumble upon any proper nouns in all this mess"), but it turned out to be completely ineffective (though apparently hilarious) when known by women...

Vaarsuvius of The Order of the Stick regularly boasts about knowing secrets that would drive lesser minds mad.

The book "Incongruity" by best-selling horror author Michael Waite in the Whateley Universe. You're fine reading it, unless you happen to know that it is really The First Scroll of The Kellith, who is prophesied to wipe mankind off the face of the earth and re-populate the planet with the seed of the Great Old Ones. It also helps not to know that Michael Waite will become The Kellith.

Pretty much anything to do with the GOO. At least one person has marveled at the fact that Hekate's brain hasn't melted out of her head yet.

This appears to have been the downfall of the Isokist, who accidentally opened the first gateway to the Great Old Ones' home dimension and paid the ultimate price for their curiosity.

Played for Laughs with Josie (nee Josh) Gillman: A Family Curse dooms most men of the Gillman line to succumb to Things Man Was Not Meant To Know. So a helpful Cosmic Horror changes Josie into a girl because, as in so many examples throughout this page, apparently woman can know them. Josie's as much confused as grateful.

In the SCP Foundation database, "[REDACTED]" merely means that the reader of the document doesn't have a sufficient security clearance to read what was blocked out. However, the term "[DATA EXPUNGED]" means that the information has been entirely removed from the Foundation's database except for a select few, and is generally unpleasing information. The trope is played straight if it appears in the description of the SCP or one of the events related to it.

Some SCPs are classified as "infohazards", which are basically this trope. They will affect anyone who knows too much about them:

One SCP will attack humans who hear or read a written description of it, and so its file has to be written in pictograms.

A different SCP will affect anyone who knows what name/term/phrase people use to refer to it. This presents a problem, since the database is setup so that for database entry "SCP-#", "SCP-#" is the name of the thing described. They get around this by making the database entry be about the building where the SCP is kept, and putting all the information about the actual SCP in a separate file. But even that isn't quite enough, since if the file referred to the SCP as "that thing", "██████", or "[REDACTED]", that would be how people refer to it, so just knowing that everyone called it "that thing" would cause a reader to be affected. Since the SCP only starts affecting a person after a month, the solution is to remove all memories about the SCP before the month is up.

SCP-096 is not an infohazard, but anybody who sees its face, whether in person, in a photograph, or a video, is going to die... because 096 will relentlessly hunt them down, kill them, and [DATA EXPUNGED] the entire corpse.

One SCP follows the concept more literally is a vending machine capable of producing any drink put into it, ranging from coffee to a "cup of Joe". One drink in particular, described as "the perfect drink", causes one to commit suicide when consumed, as the drink is so perfect that anything the drinker will experience after it will seem disappointing in comparison.

One of the many theories connected to the Slender Man is that the more you know about him, the more likely it is that you'll be next...

There's quite a few things within Night Vale which, if you value your soul, life and/or sanity, you should probably leave well enough alone. This means that while the community radio will mention things like the Dog Park and the Shape in Grove Park That No One Acknowledges or Speaks About, Cecil will finish his report by reminding listeners that they should not think or know about these things. Or else.

Western Animation

The Nightmare Realm of Gravity Falls is one of these. Fiddleford McGucket accidentally got sucked into it for a brief time, and when he came out, he was so horrifically traumatized that he deliberately and repeatedly wiped his own memory to the point of permanent brain damage, reducing him to "local kook" Old Man McGucket.

In the comics, a Guardian of the Universe (specifically Krona) found out (with severe and unpleasant consequences) and so the rest of the Guardians wanted/needed to make sure it never happened again. (Details vary depending on when the specific telling of the story was written.)

In the My Little Pony G3 film The Runaway Rainbow, when Rainbow Dash admits that she doesn't know how rainbows are made she says "Well, darlings, there are things we're not supposed to know."

In the latest incarnation of The Powerpuff Girls Fuzzy Lumpkins gets sucked through a portal via an evil tiara. After the tiara is destroyed he returns and says that he's seen things no man should ever see.

Invoked by Ray Stanz in The Real Ghostbusters episode "Who're You Calling Two-Dimensional?" After Egon runs a test to find out what's inside Slimer, Slimer gets really hot and suddenly popcorn starts popping out of Slimer and filling the room, bursting a door open in the process.

Janine: Oh my gosh! Is everybody okay? Egon: Don't Ask. Janine: What happened? Ray: We made an important discovery. We discovered there are some things that Man was not meant to know.

In Rick and Morty, this is the main reason Rick is so mentally disturbed: humanity was clearly never meant to have access to The Multiverse, encounter the horrors therein, and most importantly, face the existential nightmares it causes. He (barely) copes by being an alcoholic hedonistic sociopath.

Morty took his first steps along this path by blocking out these thoughts with the noise of mindless television and advises his sister to do the same.

The Simpsons: Apu displays in his store as part of a promotion a can without a label. Otto says a line almost exactly the same as the trope title when he comes across it.

Mr. Krabs:(tied up, while Plankton is about to read the secret Krabby Patty formula/recipe) I'm telling you! You won't be able to handle the truth! There are some things in this world that weren't meant for mortal eyes!

Plankton: I don't care! Drum roll, please! ...The secret recipe for one Krabby Patty is: a pinch of salt... three teaspoons of chopped onions... a cup of love... mixed together with the most important ingredient of all: four heaping pounds of freshly ground... (turns page, sees picture of himself) plankton!?

In a Teenage Mutant Ninja Turtles episode, this line is spoken almost word for word by a panicked Mad Scientist working for the Foot Clan in a video journal that the Turtles find, describing the Shredder's horrid genetic experiment that turned human victims into mutants. (More than likely, the scientist and all other members of the Foot are dead by now.)

Parodied in The Tick: "Let us not forget the lesson that we can learn from this, Arthur, that man was not meant to tamper with the four basic food groups."

May God help you.

Alternative Title(s):Things Man Was Not Meant To Know, Man Was Not Meant To Know, Thing Man Was Not Meant To Know

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